1. Field of the Invention
The present invention relates to a fuel cell stack structure, and more particularly, to a fuel cell stack structure in which at least one defective fuel cell among a plurality of stacked fuel cells to increase the amount of electric power is capable of being easily replaced.
2. Discussion of Related Art
Generally, a fuel cell is a generator which includes a cathode layer and an anode layer on respective surfaces of an electrolyte layer, and generates electricity by an electrochemical reaction between hydrogen and oxygen through ion conduction occurring at the electrolyte layer when an air including oxygen and a fuel gas including hydrogen are supplied to the cathode layer and the anode layer, respectively.
Such a fuel cell is a highly efficient and pollution-free generator having a simple energy conversion process and, in principle, generates energy through oxidation of hydrogen. Because of such an environmentally friendly characteristic, recently, studies of fuel cells have been actively progressing.
Particularly, among fuel cells, a solid oxide fuel cell (SOFC) is a fuel cell operated at a high temperature of approximately 600 to 1000° C. using a ceramic as an electrolyte, and has various advantages such as the highest efficiency among the various types of fuel cells including a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), a polymer electrolyte fuel cell (PEFC), etc., less pollution, and enabling combined cycle power generation without a fuel processor.
A fuel cell having a structure of an electrolyte layer, a cathode layer and an anode layer is usually called a single cell. Since electricity generated by the single cell is approximately less than 1 V, which is ineffective, a technique of increasing a generated voltage by stacking a plurality of single cells in the form of a stack structure has received attention.
In addition, consequently, with the tendency to increase the number of stacked single cells to further increase the amount of electric power generated from the stack structure, first and second separation plates electrically connected to each other are disposed between the single cells to only change a single defective cell when defects are found in the single cells. Here, in each of the first and second separation plates, an air hole and a fuel hole are disposed to provide an air and a fuel gas to the cathode layer and the anode layer, and a sealing member is disposed to seal the holes.
However, the first and second separation plates have an unstable electrical contact due to a height of the sealing member, or fine unevenness by a processing error, which is caused by a difficulty in processing the plates to a perfect plane, and have an oxidized contact surface in a space formed by the unstable contact, thereby increasing an electrical resistance between the first and second separation plates. Particularly, when the single cells are solid oxide fuel cells (SOFCs), their operating temperature are very high, for example, approximately 600 to 1000° C., and thus the contact surface may be more easily formed, thereby further increasing the electrical resistance. When the electrical resistance is increased as described above, collection efficiency of electricity generated from the single cells may be degraded.